Both within and between species, leaf physiological parameters
are strongly related to leaf dry mass per area (LMA, g/m2), which
has been found to increase from forest floor to canopy top in
every forest where it has been measured. Although vertical LMA
gradients in forests have historically been attributed to a direct
phenotypic response to light, an increasing number of recent
studies have provided evidence that water limitation in the upper
canopy can constrain foliar morphological adaptations to higher
light levels. We measured height, light, and LMA of all species
encountered along 45 vertical canopy transects across a Costa
Rican tropical rain forest. LMA was correlated with light levels
in the lower canopy until approximately 18 m sample height and
22% diffuse transmittance. Height showed a remarkably linear
relationship with LMA throughout the entire vertical canopy profile
for all species pooled and for each functional group individually
(except epiphytes), possibly through the influence of gravity
on leaf water potential and turgor pressure. Models of forest
function may be greatly simplified by estimating LMA-correlated
leaf physiological parameters solely from foliage height profiles,
which in turn can be assessed with satellite- and aircraft-based
remote sensing.